Marine jet propulsion units



0d. 17, 1967 W RR 334m MARINE JET PROPULSION UNITS Filed April 18, 1966 8 Sheets-Sheet l 1| llf Oct. 17, 1967 R. WARREN MARINE JET PROPULSION UNITS 8 Sheets-Sheet 2 Filed April 18, 1966 v Oct. 17, 3967 R. WARREN MARINE JET PROPULSION UNITS Filed April 18, 1966 8 Sheets-Sheet 3 m 17; 1967 H. mm 534m MARINE JET PROPULSION UNITS Filed April 18, 1966 s Sheets-Sheet 4 x \\\T H M I {I i i iii Filed April 18, 1966 Get. E7, 3%? R. WARREN 3,347,045

MARINE JET PROPULSION UNITS 8 Sheets-Sheet 5 r f we; A52 /56 $47 W Y Ame;

Oct. 17, 196 7 R. WARREN MARINE JET PROPULSION UNITS 8 Sheets-Sheet 6 Filed April 18, 1966 Oct. 17, 1967 R. WARREN fifiififi MARINE JET PROPULSION UNITS Filed April 18, 1966 8 Sheets-Sheet 7 giyji I Filed April 18, 1966 Oct. 17, 1 967 R. WARREN 3,347fl45 MARINE JET PROPULSION UNITS 8 Sheets-Sheet 8 F a a w 5% 7 1 I, /95 I94 W 200 "08 I. i 2041 J}; H

United States Patent 3,347,045 MARINE JET PROPULSION UNITS Reginald Warren, London, England, assignor to Cape Marine Propulsion Limited, London, England, .a corporation of Great Britain Filed Apr. 18, 1966, Ser. No. 543,153 Claims priority, application Great Britain, Apr. .27, 1965, 17 ,7 46/ 65 27 Claims. (Cl. 60222) This invention relates to jet propulsion appartus for marine craft, having a motor driven axial flow water impeller, rotatable within a tubular duct, for providing the jet thrust.

It is usual for such marine jet propulsion units to create their thrust by causing the impeller to maintain a water pressure in an after casing or duct from which it issues as a righ velocity jet. It has been found that increasing the incoming velocity to the required outlet velocity by such pressure system results in a loss of .efiicie'ncy which would not occur if the required increase of incoming velocity to outgoing velocity were obtained without recourse to pressurizing. Furthermore, such a pressurized system is more prone to cavitation or water-hammer than a non-pressurized system would be.

Accordingly it is an object of the present invention to provide a marine jet propulsion unit which overcomes the above disadvantages by progressively increasing the inlet velocity to the required outlet or jet velocity without ressurizing as above described.

It is a further object of this invention to provide control means suitable for use with the marine jet propulsion units of this invention.

According to the present invention, a jet propulsion unit comprising an axial flow impeller, an impeller duct including a frusto-conical section closely surrounding the impeller, the diameter of the frusto-conical section decreasing in the direction from the leading edges towards the trailing edges of the blades of the impeller, and at least one section selected from an inlet section, extending forwardly from the frusto-conical section, the diameter of the inlet section increasing steeply and uniformly from the frusto-conical section, and an outlet section of substantially uniform cross section extending rearwardly from the frusto-conical section, the individual length of said sections being not greater than that of the frusto-coni'cal section, and that the boss of the impeller increases in diameter from the leading edges to the 'trailin-g'edge's of blades extending from the boss.

Preferably the lengths of the inlet section (L2), the frusto-conical section (L1), the outlet section (L3), and of the impeller boss (L4) are in the following proportions:

Inlet section (L2) from 0 to 0.25 D

Frusto-conical (L1) section from 0.25 to 0.45 D

Outlet portion (L3) from 0 to0.25 D

Impeller boss (L4) from 0.25 to 0.45 D (where D is the minimum internal diameter of the duct).

.an arc of a circle of radius 1.05 to 1.25 D, centered at a point, on a straight line produced from the rear face of the boss and extending normal to the longitudinal axis 2 thereof, and spaced from said axis by a distance equal to D Preferably the angle subtended .by the internal surface of the frusto-conical section and the longitudinal axis thereof is between 10 and 20 and the angle subtended by the internal surface of the inlet section and the longitudinal axis thereof is between 25 and 35 It is further preferred that the contour of the thrust face of the impeller blades is selected such that the face of each blade lies on an arc of a circle of radius between 0.81 and 0.85 P centred on the perpendicular bisector of the pitch datum line and spaced therefrom by a distance 0.80 P, where P is the pitch of the impeller.

A portion of the thrust face of each blade, extending rearwardly from the leading edge for a distance of up to substantially one third of the width of the blade may be so formed as to lie on an arc of a circle of radius from 0.61 to 0.65 P centered on the perpendicular bisector of the pitch datum line and spaced therefrom by a distance substantially 0.60 P.

The invention is described hereinafter with reference to theaccompanying drawings in which:

FIGURE 1 is a diagrammatic sectional view of a marine jet propulsion unit mounted in a craft so as to provide a horizontally and rearwardly directed propulsion je't;

FIGURE 2 is a sectional side elevation of the propulsion unit shown in FIGURE I, mounted in ahousing within the bottom of a boat and having attached thereto jet flow control means;

FIGURE 3 is a plan view of the jet flow control means shown in FIGURE 2;

FIGURE 4 is a viewof the upstream end of thecontrol means shown in FIGURE 2; detached from the propulsion unit and observed in the direction of the arrow V in FIG. '2;

FIGURE 5 is a sectional side view of another embodiment of jet flow control means, suitable for use with the propulsion unit illustrated in FIGURE 1;

FIGURE 6 is an end view of the outlet end of the control means shown in FIGURE 5;

FIGURE 7 is a side elevation partly in section of another embodiment of a jet propulsion unit mounted vertically Within the bottom of a boat in a housing incorporating jet flow control means;

FIGURE 8 is a sectional side elevation of a further embodiment illustrating another form of housing incorporating jet flow control means;

FIGURE 9 is a side elevation partly in section of a propulsion unit mounted in a housing within the bottom of a boat, wherein the housing incorporates jet flow control means; i

FIGURE 10 is a section through the housing shown in FIGURE 7 taken upon the line VIH-VIII;

FIGURE 11 is a side elevation partly in section of a modification of the housing and control means shown in FIG. 7;

FIGURE 12 is a side elevation partly in section of a propulsion unit mounted in a housing for attachment outboard of a boat, the housing incorporating jet flow controlmeans;

FIGURE 13 is a plan view of the housing of FIGURE 12, withthe upper portion thereof removed in the interests of clarity.

Referring to FIGURE 1, the jet propulsion unit comprises an axial flow impeller 10 keyed on a shaft 11 enclosed within a duct 12 "terminating "in the jet cone.

The jet cone comprises a frusto-conical section 13, having a length L1, and within which the impeller 10 is rotable; an inlet section 14, having a length L2 and extending upstream from the section 13, and a cylindrical outlet section 15, hereinafter referred to as the snout, and having a length L3 extending downstream from the frusto-conical section 13; in the Specification and claims the terms upstream and downstream are to be understood to refer to the normal direction of flow of water through the duct produced by the impeller. The blades of the impeller 10,

one of which is shown diagrammatically at 16 are at-- taohed to a boss 17, the diameter andtr-averse area of which increases from the upstream to the downstream end.

We have discovered that by selecting the configuration and dimensions of the impeller and impeller duct within closely defined-limits the overall-efficiency of the unit can be substantially increased whilst at the same time cavitation and water hammer can be avoided. In Table I, reproducedhereunder, we have set out the preferred ranges and the optimum value withineach range.

TABLE I Preferred Optimum Range alue Minimum Internal Diameter (D) of Impeller Duct Length (L1) oi frustoconical section 0.250.45 D 0.35 D Length (L2) of inlet Section 0.10-0.25 D 0.15 D Length (L3) of outlet section--. 0.15-0.25 D 0.20 1) Length (L4) impeller boss 0.25O.45 D 0.35 D Angle B) of taper of inlet section relative 2535" 30.

to longitudinal axis of duct. Angle (a) of taper of irustro-conical section 13.

relative to longitudinal axis of duct- We have further found that in designs for high impeller speeds it is advantageous to maintain L2 at or near its maximum value while reducing L3 to zero-this helps avoid cavitation. Conversely, at low impeller speeds, it is advantageous for the highest efficiency to maintain L3 at ornear its maximum value and decrease L2 to-zero.

The impeller boss increases in diameter from its forward end such vthat, in longitudinal profile,,the external surface of the boss follows an arc A1 of a circle having a center A, and radius a, where a=from 1.05 to 1.25 D, optimally=l.15 D, center A being located on a plane Y, produced from the rear end of the boss, being perpendicular to the longitudinal axis thereof, and spaced from said axis by a distance D1 equal to D. j The face of each impeller blade increases in pitch in specific proportion related both to the increasing diameter of the boss andthe angle of taper of the frusto-conical section of the duct. In the example illustrated, the thrust wardly therefrom for a distance equal to the length of the snout section of the impeller duct.

In the propulsion unit of the present invention we have utilised a frusto-conical section to shroud the blades of the axial flow impeller, in conjunction with a boss of appropriate curved profile, since this construction considerably simplifies the production of the impeller duct as a casting and avoids the problems which would be encountered with the internal machining of the duct to produce a curved internal profile.

According to a further feature of the invention, control means suitable for use in conjunction with the jet propulsion unit hereinbefore described may comprise a tubular casing adapted to be mounted downstream of and axially alignedwith the outlet of the jet propulsion unit so as to constitute a secondary jet outlet, a steering deflector mounted within the downstream end of the tubular casing for pivotal movement about a vertical axis, valve means pivotally mounted within the tubular casing; upstream of the steering deflector for movement between a position in which the tubular casing is substantially unobstructed by thevalve means and a position in which the passage is fully obturated by the valve means, and a forwardly directed auxiliary jet outlet communicating with the tubular passage upstream of the valve means, the auxiliary jet outlet being angularly displaceable in a horizontal plane.

One example of jetflow control means will now be described. with reference to FIGURE 2, wherein there is shown a jet propulsion unit 20 of the type described and illustrated in FIGURE. 1, attached to the outlet endof a generally tubular inlet casing or housing 22 mounted in a boat, the bottom of which is denoted at B, such that the inlet aperture 24 of the casing is substantially flush with the bottom B of the boat and the outlet aperture 26 of the casing extends through the ransom T and in a substantially horizontal direction.

A control casing 28 incorporating jet flow control i in known manner a shaft gland 30 through which passes face ,of each blade from leading edge to trailing edge thereof, follows a curvature defined by intersecting arcs B1 and C1 of a circle, center B and radiusb, where b=substantially 0.62 P, and of a circle, center C and radius 0, where c==substantially 0.83 P, respectively. Center B is located at a point on a line Z perpendicularly bisectiug the pitch datum line P1 and spaced from the latter by a distance.BZ,'where BZ=substantially 0.60 P, and center C is located also on the line Z but spaced from the line PL by a distance CZ, where CZ=substantially 0.80 P, P representing the pitch of the impeller.

The jet propulsion unit of the present invention may be mounted in or attached to the hull of a craft in any suitable manner which permits a substantially unrestricted flow passage into or out of the impelelr duct. It may be for example mounted within or ahead of a jet flow control casing such as will be, described hereinafter. Where no control casing is utilised and the craft is controlled in the ahead and astern directions by means for example of rudders disposed clear of the jet stream produced by the unit, the boss of the impeller may be fitted with a cylindrical extension having a diameter equal to the rear face of the boss and extending rearthe shaft 32 of the propulsion unit 20, and additionally supports thrust bearings 34 for the impeller shaft 32.

The duct 36 of thepropulsion unit 20 is attached to .the end face of theoutlet aperture of the casing 22 by bolts 38 passed through a flange 40 on the duct 36, the

flange'40 being positioned on the duct 36 such that the greater part of the length of the duct 36 extends I631.-

.wardly beyond the outlet aperture 26 of the casing 22.

The inlet aperture of the, casing. 22 is provided with a grid or perforate screen 42 to guard against the entry of flotsam into the inlet casing, which might damage they propulsion unit. An inspection cover 44 may be provided in the upper wall of the casing 22.

The control casing 28 consists of a substantially cylindrical open ended tube'constituting a secondary jet outlet. the minimum internal diameter of which is equal to, or greater than the diameter of the outlet of the propulsion unit 20. One end portion 46 of the casing 28 has a cross sectional area enlarged with respect to that of the remainder of the casing. The end portion 46 is provided with a peripheral flange 48 by means of which the casing 28 is secured to the inlet casing 22 for example by bolts (not shown) passedthrough the flange 48, through the false transom FI and through a circumferential flange 50 provided on the inlet casing 22 adjacent the outlet 26 thereof.

When secured to the inlet casing 22, the portion 46 the impeller duct 36 and forms a watertight seal between the outlet of the propulsion unit and the passage portion 52 of the casing 28, through which the jet stream passes. The length of the end portion 46 is so selected that the upstream end of the passage 52 is spaced rearwardly of the downstream end of the duct 36 by a small gap 53, the purpose of which will be described hereinafter.

A disc valve 54 is provided within the passage portion 52, which valve is angularly displaceable about a horizontal axis 55 which extends transverse to the longitudinal axis of the passage, passing through the plane of the disc valve and the centre thereof. The disc valve is angularly displaceable by a lever arm (not shown) which may be remotely operated from for example within the boat between a position in which the disc valve lies in a horizontal plane and provides substantially no obstruction to the flow of liquid through the passage 52 and a position in which the disc valve lies in a substantially vertical plane closing the passage 52 and preventing flow of liquid therethrough.

An annular duct 56 surrounds the upstream end of the passage 52 and connects the interior of the casing 28, forward of the passage 52, with an outlet 57 in a circular plate 58 mounted in an aperture 59 formed the underside of the casing 28. The outlet 57 hereinafter referred to as astern jet is inclined downwardly at an angle of approximately to the horizontal and the plate 58 is angularly displaceable between fixed limits in a horizontal plane about a vertical pivot 61 passing through the Center of the plate 58, such that in its mid position between its limits of angular displacement the astern jet is directed forwardly beneath the boat and in one or other of its extreme limits of angular displacement, the outlet is inclined to the longitudinal axis of the boat, by for example an angle of approximately The plate 58 is connected by a linkage 60 to an ahead steering deflector plate 62 which is mounted at the downstream end of the passage 52 for movement about a vertical axis between bearings 64 formed integrally with the casing 28. The plate 62, which is generally rectangular in profile is provided with a portion 66 extending upstream of its vertical pivot axis, through the lower half of the passage 52. The portion 66 has a curved lower edge 68 and a straight horizontal upper edge 70. It will be appreciated that the omission of a corresponding upstream extension of the plate 62 in the upper half of the passage 52 enables the disc valve 54 to be angularly displaced to a horizontal position in which it overlies the upstream portion 66 of the deflector plate 62.

In the illustrated embodiment the deflector plate 62 is connected by a shaft 71 and linkage 72 (FIGURE 3) to a vertical shaft 74, movement of which is effected by a tiller or mechanical connection to a steering wheel (not shown).

For forward propulsion, the disc valve 54 is maintained in its horizontal or open position and steering of the craft is controlled by the deflector 62 in response to movements of shaft 74. It will be noted that when the deflector 62 is turned through a substantial angle, for example 35, from the fore and aft line, substantially three quarters of the jet stream is deflected by the plate 62 while the remainder is allowed 'to pass over the horizontal surface 70 of the forward extension 66 of the plate 62, thus maintaining a proportion of forward thrust while the craft is maneuvered by the deflection of the greater portion of the jet stream.

Astern propulsion of the craft is achieved by closure of the disc valve 54 which pressurizes the jet ahead of the valve and causes the jet efliux to be diverted through the annular passage 56 and discharged through the astern jet outlet 57. Steering of the craft astern is controlled by movement of the shaft 74 which is linked to the plate 58 through the linkage 72, deflector plate 62 and linkage 60. Angular displacement of the astern jet outlet 57 is thus accompanied by an equal and opposite angular movement of the deflector plate 62.

A neutral position wherein the jet flow is balanced equally between the ahead and astern outlets is obtained by suitable intermediate angular displacement of the disc valve 54.

Another embodiment of jet flow control means suitable for use with the propulsion unit of the present invention may comprise a jet thrust reversing member attached to a boats transom for pivotal movement about a horizontal axis between an inoperative position in which the reversing member is positioned above and clear of the outlet of the jet unit and an operative lowered position in which the member lies in the path traversed by the jet stream discharged from the propulsion unit, the thrust reversing member having a curved profile to deflect the jet stream downwardly and forwardly beneath the boat, a steering deflector pivotal about a vertical axis mounted between the outlet of the propulsion unit and the reversing member in its operative position, and means carried by the steering deflector for varying the angular deflection of the jet stream, deflected forwardly by the reversing member, in such a manner as to permit the craft to be steered astern. Referring to FIGURES 5 and 6 which illustrate this embodiment, elements of the propulsion unit and of the boat which are similar to those shown in FIGURES 2 to 4 are denoted by the same reference numerals.

The jet controlled means comprise a hood secured to the transom FT and a thrust reversing member which consists of a rectangular curved plate 82 and associated wing plates 84 pivotally mounted between brackets 86 carried by the transom FT beneath the hood 80, for movement about a horizontal axis 88. The reversing member 82 is pivotable (by means not shown) between a raised position in which it lies clear of and above the outlet of the jet propulsion unit 20 and a lower operative position in which the plate 82 deflects the jet stream downwardly and forwardly beneath the boat to provide astern thrust.

A steering deflector plate 90 is mounted beneath the hood 80 and between the jet outlet and the reversing member 82. The deflector 90 is movable about a vertical axis between bearings 92 and is formed with a curved trailing edge corresponding to the profile of the plate 82.

On each side of the steering deflector 90 is provided a fixed vane 94 inclined outwardly and downwardly with respect to the plane of the deflector 90 and positioned thereon so as to be beneath the path traversed by the jet stream when the reversing member 82 is in its inoperative position.

When the reversing member 82 is lowered to its operative position the jet stream is deflected downwards, striking one or other of the vanes 94 according to the angular position of the steering deflector 90 and thus obliquely deflecting the downwardly deflected jet stream to one or other side of the boat, enabling the boat to be steered while going astern.

A- further embodiment of jet flow control means for a jet propulsion unit is illustrated in FIGURE 7 and comprises a casing adapted to be mounted in an aperture in the bottom of the boat, an inlet opening in the casing containing an axial flow impeller, a flow passage extending substantially horizontally within the casing from the discharge side of the impeller, a downwardly directed outlet opening communicating with the flow passage, and a circular frame disposed within the outlet and rotatable in a horizontal plane normal to the axis of the outlet, the frame having attached thereto one or more jet deflecting blades pivotable about horizontal axes between a first operative position wherein the downwardly directed jet is deflected towards a horizontal plane and in a direction normal to the axis of the deflector or deflectors, and a second'operative position in which the jet is similarly deflected towards a horizontal plane but in a direction opposite to the first mentioned direction, and through an intermediate position wherein the jet is at least partially obturated. Referring to FIGURE 7 the casing denoted by reference is rectangular in plan and is provided with a vertical inlet 142 communicating with a horizontal flow passage 144 and a vertical outlet 146. The inlet 142 is in the form of a frusto-conical duct and surrounds the impeller 148 of the jet propulsion unit, the drive shaft 150 of which extends vertically upwardsthrough the flow passage 144 and the top of the casing 140, being connected in known manner to a driving motor 141. Within the outlet 146 is mounted a control device consisting of a circular rotatable frame 152 supporting deflectors 154, each of which comprises a rectangular oblong plate curved along its shorter axis. The deflectors 154 are spaced parallel to each other within the frame 152 and are pivotable about a horizontal axis 156, by means of an interconnecting linkage 158. The rotatable frame 152 is secured to a hollow shaft 160 which extends upwards through the flow passage 144 and the casing 140 for connection by any suitable means to the steering mechanism of the craft. A flexible cable 162 passes through the hollow shaft 160 and is'connected to the center deflector 164. It will thus be apparent that by movement of the deflectors 154 about their pivot axis 156 and by rotation of the frame 152 through an angle of substantially 90 on either side of the longitudinal axis of the casing 148, the jet stream may be deflected in any desired direction towards a horizontal plane thus enabling the craft to be propelled in the desired direction. If the deflectors 154 are displaced to an intermediate position in which they lie in substantially horizontal planes the jet stream is partially obturated, providing a neutral position wherein'the propulsive thrust in any one direction is counterbalanced by an equal and opposite thrust in the opposite direction.

A further embodiment of jet flow control means is diagrammatically illustrated in FIGURE 8 and comprises an axial-flow impeller rotatable about a vertical axis within an impeller duct, the upper and lower ends of which constitute respectively an inlet to and a discharge outlet from the impeller, a conicalflow casing open at its base and surrounding the impeller and duct, the casing being spaced from the duct so as to define a vertical annular passage through which water may be drawn into the impeller inlet, for subsequent discharge downwardly through saidduct, and jet deflecting means rotatably mounted beneath the impeller duct and arranged to deflect the jet discharged therefrom into a substantially horizontal plane and in any desired direction therein.

FIGURE 8 illustrates a vertically mounted jet propulsion unit located in an aperture provided in the bottom of a boat. A substantially conical open-bottomed casing 170 surrounds and supports an impeller 172 which is driven through a vertical shaft 174 extending upwardly through a mounting plate 176, the shaft 174 being connected to a driving motor 177 mounted on the plate 176.

The impeller 172 is surrounded by a conical duct 178 which in turn is supported by longitudinals 180 extending across the open bottom of the casing 170. The space between the duct and the side wall 182 and the casing defines an annular inlet 183 up through which water may be drawn by the impeller and expelled downwardly through the duct in the form of a jet.

A rotatable ring 84 carrying a set of deflector blades 186 is mounted beneath the impeller, the blades 186 being arranged to deflect the jet issuing from the duct 17 8 through substantially a right angle so that the jet is discharged in a horizontal plane in a direction determined by the angular rotation of the ring 184. A shaft 188 in geared connection with the ring 184 and extending vertically upward through the casing 170 for connection to the tiller or steering wheel of the boat, enables the ring 184 to be rotated through 360 thus permitting maneuverability in any direction.

In another embodiment according to our invention, jet flow control means for a marine jet propulsion unit, including an axial flow impeller comprise at least one jet reversing deflector disposed downstream of the outlet of the propulsion unit, the or each deflector being pivotable about a horizontal axis normal to the axis of the jet outlet and at least one steering deflector disposed beneath the reversing deflector and pivotable about an axis parallel to the axis of the jet outlet, a flow casing surrounding the impeller and deflectors, and the impeller being rotatable within a conical duct. Preferably the periphery of the duct is spaced from the surrounding casing. Referring to FIGURES 9 and 10 the jet propulsion unit, which includes an impeller within a conical'duct102, is located within a tunnel shaped flow casing 104, which in turn is mounted in an aperture, the forward end of which is indicated at F, formed in the bottom of a boat. The

housing 106 of the impeller shaft extends through the forward end wall 108 of the casing whereby the shaft may be connected to a motor within the boat. The underside 110 of the casing is open and is covered by an open mesh grid 112 which permits a substantially unimpeded flow of water through the casing but prevents debris from being drawn into the impeller. The impeller duct 102 is spaced from the surrounding wall of the casing 104 by an annular or part annular gap 105 through which water can freely flow when the craft is under way.

Rearwardly of the impeller 100 are mounted first and second pairs of jet deflectors indicated in FIGURES 9 and 10 at 114 and 116 respectively. The deflectors 114 which are in the form of oblong rectangular blades are spaced one from the other along the longitudinal axis of the In the positions 114' shown in dotted line in FIGURE 9, to which the deflectors 114 can be pivoted by the external linkage, the deflectors 114 substantially obturate the downstream end 120 of the casing 104 and deflect the jet stream produced by the impeller 100 in a downward and forward direction indicated by the arrow Z, thus providing astern propulsive thrust to the craft.

Steering of the craft is achieved both when going ahead or astern by means of the second pair of deflectors 116, between and past which the jet stream produced by the impeller 100 is directed when the deflectors 114 are in either of the positions shown in FIGURE 9. The deflectors 116 are mounted side by side and parallel to each other beneath the deflectors 114 between brackets 122 and are capable of pivotal movement about horizontal axes parallel to the longitudinal axis of the casing i.e. at right angles to the pivotal axes of the deflectors 114. The deflectors 116 are movable, by a linkage (not shown) connected to the tiller or steering wheel of the craft, between -planes inclined to either side of a vertical plane, such that when the deflectors 116 are vertical, the, jet

stream is discharged either directly ahead or astern, ac-- cording to the position of the deflectors 114 and if the deflectors 116 are moved toone side or other of the vertical the jet stream will be diverted so as to give a corresponding sideways component of thrust thus enabling the craft to be steered, either ahead or astern.-

By positioning the deflectors 114 in an intermediate or neutral positionin which a proportion only of the jet stream is diverted forwardly, while the remainder continues to be discharged rearwardly, the output of the jet propulsion unit may be so balanced as to maintain the craft stationary, without the-need to stop or unclutch the motor which drives the jet propulsion unit.

FIGURE 11 illustrates a control casing similar to that shown in FIGURES 9 and 10 but modified for use with a jet propulsion unit which is reversible, so that the jet stream may be discharged from either the forward or after end of the impeller duct, In FIGURE 11 elements which are the same or similar to those depicted in FIG- URE 9 are identified by the same references distinguished by a tick. The impeller 100' and conical duct 102' are mounted in a similar manner to that shown in FIGURE 9 but in place of the deflectors 114 and 116 there is provided a pair of steering deflectors 130 and 132 respectively positioned forward of and abaft the impeller 100 and angularly displaceable respectively about generally vertical axes normal to the axis of the impeller 100', the pivot axis of the deflector 132 being defined by a shaft 134 which extends through the upper side 104 of the casing, which shaft 134 passes through a watertight gland 136. The deflector 130 which is mounted between bearings 135 is connected to the deflector 132 by linkage 138 such that angular displacement of the shaft 134 produces a deflection of the deflector 130 equal to and in the opposite direction to the deflection of the deflector 132.

It will be apparent that in operation, a steering surface i.e. deflector 130 or 132 is located within the jet stream produced by the impeller 100' irrespective of the direction of rotation of the latter. This arrangement enables the craft to be steered whilst proceeding either ahead or astern. Means may be provided for disconnecting the deflector 130 from the deflector 132 and for locking the forward deflector in a fore and aft position while the craft is being propelled ahead.

FIGURES 12 and 13 illustrate a jet propulsion unit and associated control means, adapted to be attached to the transom of the boat in the manner of a conventional marine outboard motor. A vertical shaft 190 is fitted in a tubular housing 192 which at its upper end supports a motor (not shown) and at its lower end is provided with a casing 194 in the form of an elbow. The casing comprises a conical vertical inlet duct 196 communicating with a horizontally directed outlet 198 for ahead propulsion and also with inclined out-lets 200 for astern propulsion, which latter extend in directions substantially opposite to the ahead outlet 198 and on either side of respectively the inlet duct 196.

The shaft 190 which projects downwardly into the casing 194 carries at its lower end an impeller 202 for rotation within the conical duct 196. The discharge through the outlets 198 and 200 of the jet stream created by the impeller is controlled by a valve 204 disposed in the outlet 198 and pivotable by means of an operating rod 206 connected to the tiller (not shown) about a horizontal axis 208 transverse to the axis of the outlet 198.

The valve 204, in the position shown in firm line in FIGURE 12, provides a substantially unobstructed passage for water through the outlet 198 but when pivoted through 90 to the position shown in dotted line at 204a, the outlet 198 is obturated and the water within the casing is pressurized ahead of the valve 204 and discharged through the astern outlets thus providing astern propulsive thrust.

' The valve 204 may be placed in an intermediate or neutral position in which the jet thrust from the ahead outlet 198 is balanced by an equal and opposite thrust from the astern outlets 200 thus obviating any need to stop or unclutch the engine when the boat is to be kept stationary.

' Steering ahead or astern is achieved in known manner, the housing carrying the motor and control casing being pivotable on the transom of the boat by means of a tiller, it may be arranged that vertical movement of the tiller controls the movement of the valve 204.

In each of the embodiments described with reference to FIGURES 2 and 12 the impeller and conical duct will utilise the configuration described hereinbefore with reference to FIGURE 1.

' In those of the foregoing embodiments wherein the control casing is arranged to be mounted within or rigidly attached to the hull of a craft, it is to be understood that the shell of the control casing may be formed integrally with the structure of the hull.

What is claimed is:

1. A jet propulsion unit comprising an axial flow impeller, an impeller duct including a frusto-conical section closely surrounding the impeller, the diameter of the frusto-conical section decreasing in the directionfrom the leading edges towards the trailing edges of the blades of the impeller, and at least one section selected from an inlet section, extending forwardly from the frusto-conical section, the diameter of the inlet section increasing steeply and uniformly from the frusto-conical section, and an outlet section of substantially uniform cross section extending rearwardly from the frusto-conical section, the individual length of said sections being not greater than that of the frusto-conical section, and that the boss of the impeller increases in diameter from the leadingedges to the trailing edges of blades extending from the boss.

2. A jet propulsion unit as claimed in claim 1, wherein the length L1 of the frusto-conical section is between 0.25 D and 0.45 D, the length L2 of the inlet portion is between 0 and 0.25 D, the length L3 of the outlet section is between 0 and 0.25 D, and the length L4 of the impeller boss is between 0.25 D and 0.45 D, where D is the minimum internal diameter of the duct, L1 and L2 being increased towards their maxima when L3 is decreased towards 0, and L3 being increased towards its maximum when L2 is decreased towards zero.

3. A jet propulsion unit according to claim 2, in which L2 is between 0.10 D and 0.25 D and L3 is between 0.15 D and 0.25 D.

4. A jet propulsion unit as claimed in claim 3, wherein the length L1 is substantially 0.35 D, the length L2 is substantially 0.15 D, the length L3 is substantially 0.20 D and the length L4 is substantially 0.35 D.

5. A jet propulsion unit as claimed in claim 2 wherein the angle at subtended by the internal surface of the frusto-conical section and the longitudinal axis thereof is between 10 and 20 and the angle ,8 subtended by the internal surface of the inlet portion and the longitudinal axis thereof is between 25 and 35.

6. A jet propulsion unit as claimed in claim 3 wherein the angle a subtended by the internal surface of the frustoconical section and the longitudinal axis thereof is betwen 10 and 20 and the angle 5 subtended by the internal surface of the inlet portion and the longitudinal axis thereof is between 25 and 35 7. A jet propulsion unit as claimed in claim 6 in which the angle on is substantially 13 and the angle ,8 is substantially 30.

8. A jet propulsion unit as claimed in claim 2 wherein the longitudinal profile of the impeller boss lies on an arc A1 of a circle of radius between 1.05 and 1.25 D centred at a point on a straight line produced from the rear face of the boss and extending normal to the longitudinal axis thereof and spaced from said axis by a distance equal to D.

9. A jet propulsion unit as claimed in claim 8 in which the radius of said are is substantially 1.15 D.

10. A jet propulsion unit as claimed in claim 2 in which the contour of the thrust face of the impeller blades is selected such that the face of each blade lies at least in part on an arc of a circle of radius between 0.81 and 0.85 P centred on the perpendicular bisector of the pitch datum line and spaced therefrom by a distance substantially 0.80 P, where P is the pitch of the impeller.

11. A jet propulsion unit as claimed in claim 2 in which the thrust face of each blade from leading edge to trailing edge thereof follows, at least adjacent said leading and trailing edges, respectively a curvature defined by an arc C1 of a circle, centre B and radius b, where b=substantially 0.62 P, and an arc C1 of a circle centre C and radius 0, where c=substantially 0.83 P, respective- 11 y, secting the pitch datum line and spaced from the latter by a distance of substantially 0.60 P and center C being located on the same line but spaced from the pitch datum line by a distance substantially 0.80 P, P representing the pitch of the impeller.

12. A jet propulsion unitas claimed in claim 1 in which the thrust face of each impeller blade comprises a plane surface.

13. A jet propulsion unit according to claim 1 including jet flow control means comprising a passage downstream of the impeller duct and deflector means. pivotally attached to said propulsion unit for movement into a position at least partially obstructing said passage.

14. A jet propulsion unit as claimed in claim 12, including control means comprising a tubular casing adapted to be mounted downstream of and in axial alignment with the outlet of the jet propulsion unit so as to con stitute a secondary jet outlet, a steering deflector mounted within the downstream end of the casing for pivotal movement about a vertical axis, valve means pivotally mounted within the casing upstream of the steering deflector for movement between a position in which the tubular casing is substantially unobstructed and a position in which it is substantially obturated, and a forwardly directed auxiliary jet outlet communicating with the tubular casing upstream of the valve means, the auxiliary jet outlet being angularly displaceable in a horizontal plane.

15. Jet flow control means as claimed in claim 14 in which the valve means is effective when the secondary jet outlet is obturated to pressurize the jet stream upstream of the 'valve means and to cause discharge of the pressurized jet stream through the forwardly directed auxiliary jet outlet so as to provide propulsive thrust 'for astern movement.

16. Jet flow control means as claimed in claim 14 in which the auxiliary jet outlet communicates with the tubular casing through an annular duct surrounding the upstream portion of the tubular casing.

17. Jet flow control means as claimed in claim 14 inv which the auxiliary jet outlet is connected to the steering deflector by a linkage arrangedto effect simultaneous and equiangular displacement of the auxiliary jet outlet in response to displacementof the deflector.

18. Jet flow control means as claimed in claim 14 wherein the valve means comprises a disc pivotable about a horizontal axis normal to the axis of the second.- ary jet outlet, the steering deflector having a portion extending upstream of its pivotal axis which portion is overlain by the disc when the latter lies in a horizontal plane.

19. A jet propulsion unit according to claim 12 having a discharge outlet extending in a substantially horizontal direction through the transom of a boat, said means comprising a jet reversing member for attachment to the boats transom for pivotable movement about a horizontal axis.

between an inoperative position in which. the reversing member is positioned above and clear of the discharge out let and an operative lowered position in which the reversing member lies in the path traversed by the jet stream discharged from the outlet, the reversing member having a curved profile for deflecting the jet stream downwardly and forwardly beneath the boat so as to provide astern propulsive thrust, a steering deflector mounted for pivotal movement about a vertical axis between the discharge outlet and the reversing member in its operative position and in the path of the jet stream, and means carried by the steering deflector for obliquely deflecting the jet stream downwardly deflected by the reversing member when in its operative position, in such a manner as to providea component of propulsive thrust directed towards one or other side otthe boat whereby the craft may be steered while proceeding astern.

20. A jet propulsion unit as claimed in claim 18 in.

which the steering deflector is provided on each side with center B being located on a line perpendicularly bi-- a fixed vane inclined outwardly and downwardly with.

traversed by the jet stream when the reversing member.

is in its inoperative position.

21. A jet propulsion unit as claimed in claim 13, said jet flow control means comprising at least one jet reversing deflector dis-posed downstream of the impeller, the or each deflector being pivotable about a horizontal axis or axes normal to the impeller axis and at least one steering deflector disposed beneath the reversing deflector or deflectors and pivotable about an axis substantially parallel to the impeller axis, within a conical duct and together with being mounted within a flow casing.

22. A jet propulsion unit as claimed in claim 21 wherein at least the discharge end of said conical duct is spaced the deflectors from the wall of the flow casing so as to define an annular flector causes an opposite and equiangular deflection of the other deflector.

24. A jet propulsion unit as claimed in claim 13, said jet,

flow control means comprising a flow passage extending substantially horizontally within the casing from the discharge side of the impeller, a downwardly directed outlet communicating with the flow passage and a frame disposed within the outlet and rotatable therein in a horizontal plane normal to the axis of the outlet, the frame having attached thereto one or more jet deflecting blades pivotable about a horizontal axis or axes and between a I first operative position wherein the downwardly directed jet emerging from said outlet is deflected towards'a horizontal plane and in a direction normal to the longitudinal axis of the or each deflector and a second operative position in which the jet is similarly deflected towards said horizontal plane but in a direction opposite to said first mentioned direction.

25. A jet propulsion unit ascIaimed in claim 20 wherein the or each deflector is pivotable through an intermediate operative position wherein the outlet aperture is at least partially obturated, and wherein the angle through which the frame is rotatable is restricted to substantially A jet propulsion unit as claimed in claim 13, comprising a conical flow casing open at itsbase and surroundingthe impeller and duct which have a verticalaxis, the casing being spaced from the duct-so. as to define a vertical annular passage through which water may be drawn into.

the impeller inlet for subsequent downward discharge through the impeller duct, and jet deflecting means rotatably mounted beneaththe impeller duct and arranged to deflect the jet discharged therefrom into a substantially horizontal plane. and in any desired directiontherein.

27. A jet propulsion unit 'accordingto. claim 13 for external attachment to the transom of a boat said unit comprising a casing defining. a tubular flow passage including a substantially vertical impeller duct and a substantially horizontally directed outlet duct, a pair of auxiliary outlets communicating with said flow passage,

downstream of said impeller and extending on either side of said inlet duct and in directions substantially opposite to the horizontally directed outlet duct and valve means mounted for pivotal movement within said horizontal.out-. let duct between a first operative position wherein the horizontal outlet is unobstructed and the auxiliary jet outletsare obturated and a second operative position in which the impeller being rotatable 13 the horizontal outlet is substantially obturated and jet flow through said casing is diverted to be discharged through said auxiliary outlets.

References Cited UNITED STATES PATENTS 1,519,580 12/1924 Gill 60-222 2,965,065 12/1960 Tinker l03-89X CARLTON R. CROYLE, Primary Examiner. 

1. A JET PROPULSION UNIT COMPRISING AN AXIAL FLOW IMPELLER, AN IMPELLER DUCT INCLUDING A FRUSTO-CONICAL SECTION CLOSELY SURROUNDING THE IMPELLER, THE DIAMETER OF THE FRUSTO-CONICAL SECTION DECREASING IN THE DIRECTION FROM THE LEADING EDGES TOWARDS THE TRAILING EDGES OF THE BLADES OF THE IMPELLER, AND AT LEAST ONE SECTION SELECTED FROM AN INLET SECTION, EXTENDING FORWARDLY FROM THE FRUSTO-CONICAL SECTION, THE DIAMETER OF THE INLET SECTION INCREASING STEEPLY AND UNIFORMLY FROM THE FRUSTO-CONICAL SECTION, AND AN OUTLET SECTION OF SUBSTANTIALLY UNIFORM CROSS SECTION EXTENDING REARWARDLY FROM THE FRUSTO-CONICAL SECTION, THE INDIVIDUAL LENGTH OF SAID SECTIONS BEING NOT GREATER THAN THAT OF THE FRUSTO-CONICAL SECTION, AND THAT THE BOSS OF THE IMPELLER INCREASES IN DIAMETER FROM THE LEADING EDGES TO THE TRAILING EDGES OF BLADES EXTENDING FROM THE BOSS.
 12. A JET PROPULSION UNIT AS CLAIMED IN CLAIM 1 IN WHICH THE THRUST FACE OF EACH IMPELLER BLADE COMPRISES A PLANE SURFACE.
 14. A JET PROPULSION UNIT AS CLAIMED IN CLAIM 12, INCLUDING CONTROL MEANS COMPRISING A TUBULAR CASING ADAPTED TO BE MOUNTED DOWNSTREAM OF AND IN AXIAL ALIGNMENT WITH THE OUTLET OF THE JET PROPULSION UNIT SO AS TO CONSTITUTE A SECONDARY JET OUTLET, A STEERING DEFLECTOR MOUNTED WITHIN THE DOWNSTREAM END OF THE CASING FOR PIVOTAL MOVEMENT ABOUT A VERTICAL AXIS, VALVE MEANS PIVOTALLY MOUNTED WITHIN THE CASING UPSTREAM OF THE STERRING DEFLECTOR FOR MOVEMENT BETWEEN A POSITION IN WHICH THE TUBULAR CASING IS SUBSTANTIALLY UNOBSTRUCTED, AND A POSITION IN WHICH IT IS SUBSTANTIALLY OBTURATED, AND A FORWARDLY DIRECTED AUXILIARY JET OUTLET COMMUNICATING WITH THE TUBULAR CASING UPSTREAM OF THE VALVE MEANS, THE AUXILIARY JET OUTLET BEING ANGULARLY DISPLACEABLE IN A HORIZONTAL PLANE. 